There are oil well drilling rigs now available to drill up to depths past 30,000 feet. To drill to these depths, the drawworks and derrick must work with tremendous weights of drill pipe extending from the surface to those depths.
The drawworks and derrick having the load capability of working the drill string to past the 30,000 foot level is still short of the capability of working the required casing string which can have a weight up to 1,000 tons. Of course, the drawworks and derrick could be built to support up to 1,000 tons of casing string, but its capacity would not only be uneconomical for the drilling operation, but would seriously lower the drilling efficiency of the rig.
It is well known to mount a hydraulic casing jacking system adjacent the well bore and within the drilling derrick. With a separate source of hydraulic power fluid, this casing jacking system has the capacity to work the casing string within the well bore. Inarguably, when the hydraulic system is operative, it assumes the duty of raising and lowering the casing string from the drilling derrick and drawworks. However, this system has all of the disadvantages and vulnerability of hydraulic systems.
It is proposed that a mechanical linkage between the casing string and the drilling drawworks be established. With the advantage of a mechanical linkage actuated by the drilling rig, the hydraulic system can be effectively supplanted. In other words, the hydraulic system can be effectively eliminated with a mechanical system which is comparably efficient to the hydraulic system, a good deal less expensive, a good deal less vulnerable to malfunction, and easier to transport and set at the well bore.